The invention relates to a roll for the pressure treatment of webs of material.
Such a roll is known from German Pat. No. 27 44 524. Pressure liquid in a longitudinal chamber in a hollow roll exerts a uniform hydraulic pressure against the inside circumference of the hollow roll, whereby the line pressure in the rolling gap is brought about. A stationary crosspiece extending through the hollow roll for supporting the roll bends under the distributed hydraulic load without making contact because of the spacing at the inside circumference of the hollow roll. In this manner the hollow roll can largely be kept free of bending due to the load.
In most cases, the important point is to be able to exert forces as large as possible with a relatively small hydraulic pressure. Longitudinal seals engaging the inside circumference of the hollow roll are arranged at the point of greatest width opposite each other or shifted 180.degree. relative to each other on both sides of the crosspiece. The pressures in the longitudinal chamber are normally in the range between 0 and 3 bar. The seal at the transverse end seals and the longitudinal seals of the longitudinal chamber need not be hermetic. Pressures of the order of magnitude given can be maintained at a hydrodynamic equilibrium with an acceptable pump output even if small amounts of leakage liquid continuously emerge at the seals. This leaking liquid accumulates in the space between the crosspiece and the inside circumference of the hollow roll, outside of the longitudinal pressure chamber. This space is therefore filled soon with leakage liquid.
If the longitudinal pressure chamber opposite the longitudinal chamber is filled with leakage liquid, heavy turbulence arises within the pressure liquid because the liquid is taken along at the rapidly revolving inside circumference of the hollow roll; this turbulence consumes the preponderant part of the driving power of such a roll, especially at higher speeds. Provision is therefore made that the opposite longitudinal chamber is not filled with liquid. This purpose is served by guide surfaces or resilient strips which wipe off the liquid adhering to the inside circumference of the hollow roll close to the longitudinal seals and direct the fluid immediately into suitable discharge or suction canals.
In the known embodiment, the guide surfaces are directly attached to the crosspiece and either rest lightly against the inside circumference of the hollow roll or are spaced a very small distance from the inside circumference. In as much as crosspiece is bent up to 30 mm inside the hollow roll for long rolls and large loads, it is not easy to assure over the length of the roll sufficiently uniform contact of the guide surfaces in tape or strip form at the inside circumference of the hollow roll. The fastening point and the contact point change their mutual position considerably under such deflections, and the guiding surface should be in a position to bridge such changes by elastic deformation. The guide surfaces then either rest too firmly against the inside circumference of the hollow roll and wear rapidly, or they are lifted in the center where the greatest spacing change takes place off the inside circumference of the hollow roll and no longer fulfill their function.
These problems become more difficult if rolls are involved which do not have mutually opposite longitudinal seals but rather relatively closely adjacent longitudinal seals in the vicinity of the rolling gap which are removed from each other only by a circumferential angle of exemplarily 30.degree. to 40.degree. and define a correspondingly narrow longitudinal chamber. Such roll designs are employed in the paper industry, if applications with particularly high web velocities up to the order of magnitude of 2,000 m/min are involved. With a narrow chamber the turbulence losses in the pressure liquid contained therein can be kept lower.
Since the guide surfaces must be adjacent to the longitudinal seals and the longitudinal seals are situated in such rolls which are known from German Auslegeschrift No. 24 61 914, in the vicinity of the action plane, i.e., in the vincinity of the plane going through the axis of the roll and its counter roll, the guide surfaces are subjected, if the cross piece is bent, to practically the full excursion, i.e., the full change of spacing between the ends of the cross piece and the zone in the center which is farthest away from the inside circumference of the hollow roll. A suitable structure of the guide surfaces to maintain a still usable contact or near-contact between their fastening points and the points of contact with the inner circumference of the roll particularly for such changes of spacing is especially difficult to design.
This design problem concerns, however, not only the guiding surfaces but also the longitudinal seals which in this case can no longer be realized by L-shaped seals according to German Pat. No. 11 93 739 but as strip gaskets in the manner shown in German Auslegeschrift No. 24 61 914 which can be dislocated in planes located parallel through the action plane against the inside circumference of the hollow roll. It is not easy to design seals of this kind which can accommodate a stroke or shift of 30 mm and more and which are furthermore free of vibration phenomena which can be generated by the inside circumferential surface sliding past in the transverse direction at high speed.
It is an object of the invention to develop a roll of the above described type so that the guiding surfaces as well as the longitudinal seals can tightly cooperate without jamming, and regardless of vibration with the inside circumference of the hollow roll even if the crosspiece is bent substantially within the hollow roll and with a corresponding change of spacing between the cross piece and the inside circumference of the hollow roll.